<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>
  <canvas id="canvas" width="400" height="400">
    此浏览器不支持canvas
  </canvas>
</body>
</html>
<script>

  const ctx = document.getElementById('canvas')

  const gl = ctx.getContext('webgl')

  // gl.clearColor(1.0,0.0,0.0,1.0) // red 1.0  green 0.0  blue 0.0 alpha 1.0

  gl.clear(gl.COLOR_BUFFER_BIT)

</script>
